[SCSI] sd: add fix for devices with last sector access problems

This patch adds a new scsi_device flag (last_sector_bug) for devices
which contain a bug where the device crashes when the last sector is
read in a larger then 1 sector read.

This is for example the case with sdcards in the HP PSC1350 printer
cardreader and in the HP PSC1610 printer cardreader.
Signed-off-by: Hans de Goede <j.w.r.degoede@hhs.nl>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/sd.c

@@ -395,6 +395,15 @@ static int sd_prep_fn(struct request_queue *q, struct request *rq)
 		goto out;
 	}
 
+	/*
+	 * Some devices (some sdcards for one) don't like it if the
+	 * last sector gets read in a larger then 1 sector read.
+	 */
+	if (unlikely(sdp->last_sector_bug &&
+	    rq->nr_sectors > sdp->sector_size / 512 &&
+	    block + this_count == get_capacity(disk)))
+		this_count -= sdp->sector_size / 512;
+
 	SCSI_LOG_HLQUEUE(2, scmd_printk(KERN_INFO, SCpnt, "block=%llu\n",
 					(unsigned long long)block));
 

include/scsi/scsi_device.h

@@ -139,6 +139,7 @@ struct scsi_device {
 	unsigned fix_capacity:1;	/* READ_CAPACITY is too high by 1 */
 	unsigned guess_capacity:1;	/* READ_CAPACITY might be too high by 1 */
 	unsigned retry_hwerror:1;	/* Retry HARDWARE_ERROR */
+	unsigned last_sector_bug:1;	/* Always read last sector in a 1 sector read */
 
 	DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */
 	struct list_head event_list;	/* asserted events */